Typically above 60,000ft (FL600) is considered to be outside of a nation's airspace[1] (by ICAO at least) - which is one of the reasons why the U2 was designed to cruise at 60,000-70,000ft (FL600-FL700). The SR-71 could cruise up to 85,000ft (FL850).
So, technically and at least according to ICAO, these birds flew/fly above a nation's sovereign airspace. That doesn't stop a nation-state from attempting to down one of these birds, of course.
60,000 feet is the limit of controlled airspace, i.e. if you fly above it air traffic control will not guide you to make sure you don't collide with other aircraft. It's not related to sovereign airspace, the area where a country has the right to decide who may fly.
I think the general rule is that sovereign airspace covers air-breathing planes but not spacecraft. From your link:
> There is no international agreement on the vertical extent of sovereign airspace, with suggestions ranging from about 30 km (19 mi)—the extent of the highest aircraft and balloons—to about 160 km (99 mi)—the lowest extent of short-term stable orbits. The Fédération Aéronautique Internationale has established the Kármán line—at an altitude of 100 km (62 mi)—as the boundary between the Earth's atmosphere and outer space, while the United States considers anyone who has flown above 80 kilometres (50 mi) to be an astronaut.
So, technically and at least according to ICAO, these birds flew/fly above a nation's sovereign airspace. That doesn't stop a nation-state from attempting to down one of these birds, of course.
[1] https://en.wikipedia.org/wiki/Airspace